Semi-active mooring recovery device and control method

Abstract

This invention relates to the field of marine renewable energy engineering technology. In order to provide a mooring system with forward-looking capabilities and relatively low energy consumption, this application provides a semi-active restoring mooring device and control method. By monitoring the motion state of the object to be balanced, its displacement in the near future is predicted, and tension is applied to the mooring cable in a specific direction in advance, thereby providing an optimal restoring force with forward-looking capabilities and directional adaptability. Since the mooring cable can be tensioned / released only when needed, and the tensioning actuator uses a hydraulic servo actuator, an electric servo cylinder, or a linear motor actuator, the energy consumption is extremely low, which is more in line with the economic requirements of long-term, unmanned operation of floating wind turbines.

Description

Technical Field

[0001] This invention relates to the field of marine renewable energy engineering technology, specifically a semi-active mooring recovery device and control method. Background Technology

[0002] Floating wind turbines are key equipment for developing deep-sea wind energy resources. Unlike fixed-foundation wind turbines, floating platforms experience six degrees of freedom of motion (sway, roll, heave, pitch, pitch, and yaw) under the influence of complex environmental loads such as wind, waves, and currents. Excessive motion, especially deviations from the horizontal plane (sway and pitch), can severely affect the structural safety of the turbine tower, power generation efficiency, and the lifespan of the transmission system.

[0003] Currently, floating wind turbines generally employ passive mooring systems, such as anchor chains, steel cables, or synthetic fiber cables. These systems provide restoring forces through the system's own gravity, buoyancy, and elastic deformation, allowing the turbine to slowly return to its center position after deviating from its equilibrium position. However, passive mooring systems have inherent drawbacks:

[0004] 1. Lag: The restoring force is generated only after the wind turbine has shifted, and it is impossible to predict or suppress larger shifts that are about to occur.

[0005] 2. Fixed Stiffness: The mooring stiffness is basically fixed after design and installation, and cannot be optimized and adjusted according to different sea states and wind turbine operating conditions. In severe sea states, insufficient restoring force may lead to excessive displacement; in normal sea states, excessive restoring force may lead to accelerated fatigue damage to the mooring system.

[0006] 3. Isotropic: Traditional symmetrical mooring systems provide restoring force characteristics that are basically the same in all directions, and cannot be reinforced for extreme loads in specific directions (such as extreme wind and wave directions).

[0007] To overcome the shortcomings of passive mooring, some active mooring technologies have been proposed, such as using thrusters or underwater robots for dynamic positioning. However, these solutions are extremely energy-intensive, economically inefficient, and difficult to apply to floating wind turbines that operate for extended periods. Summary of the Invention

[0008] In order to provide a mooring system with forward-looking design and relatively low energy consumption, this application provides a semi-active mooring recovery device and control method.

[0009] The technical solution adopted by the present invention to solve the above problems is:

[0010] A semi-active restoring mooring device includes an array of mooring cables, one end of which is connected to the object to be balanced, and the other end of which is connected to an anchoring foundation on the seabed. It also includes:

[0011] A positioning unit installed on the object to be balanced is used to monitor the displacement and motion status of the object in real time.

[0012] The controller is used to predict the displacement of the object to be balanced at the next moment based on the displacement data collected by the positioning unit; and to calculate the total restoring force vector required to restore the object to the equilibrium position based on the predicted displacement; and to decompose the total restoring force vector into control commands for each tensioning actuator.

[0013] The tensioning actuator corresponds one-to-one with the mooring cable and is used to adjust the tension state of the corresponding mooring cable according to control commands.

[0014] Furthermore, the tensioning actuator is a hydraulic servo actuator, an electric servo cylinder, or a linear motor actuator.

[0015] Furthermore, the object to be balanced is a floating wind turbine platform.

[0016] Furthermore, the positioning unit employs a combined navigation system that integrates real-time dynamic carrier phase differential technology and an inertial measurement unit.

[0017] Furthermore, the mooring cable is connected to the object to be balanced via a universal joint.

[0018] A semi-active mooring recovery device control method, applied to a semi-active mooring recovery device, including:

[0019] The displacement data sequence of the object to be balanced is acquired in real time, and the displacement of the object to be balanced at the next moment is predicted based on the acquired displacement data sequence; the total restoring force vector required to restore the object to the equilibrium position is calculated based on the predicted displacement; the total restoring force vector is decomposed into control commands for each tensioning actuator; the tensioning actuator adjusts the tension state of the corresponding mooring cable according to the control commands.

[0020] Furthermore, the specific method for predicting the displacement of the object to be balanced at the next moment based on the collected displacement data sequence is as follows: ,in, This is the predicted displacement vector at time k+1. , , Let be the actual displacement vectors at times k, k-1, and k-2, respectively. Let be the acceleration vector at time k. These are the weighting coefficients.

[0021] Furthermore, it also includes adjusting the weighting coefficients based on the measured displacement values.

[0022] Furthermore, when decomposing the total restoring force vector into control commands for each tensioning actuator, it also includes obtaining the optimal control command with the goal of minimizing total energy consumption or achieving the most balanced tension in each cable.

[0023] The advantages of this invention compared to the prior art are: by monitoring the motion state of the object to be balanced, its displacement in the short term can be predicted, and tension can be applied to the mooring cable in a specific direction in advance, thereby providing an optimal restoring force with foresight and directional adaptability; since the mooring cable can be tensioned / released only when needed, and the tensioning actuator uses a hydraulic servo actuator, electric servo cylinder or linear motor actuator, the energy consumption is extremely low, which is more in line with the economic requirements of long-term, unmanned operation of floating wind turbines. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of a semi-active mooring recovery device.

[0025] Figure 2 This is a flowchart of the semi-active mooring recovery device control method. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0027] A semi-active restoring mooring device includes an array of mooring cables, one end of which is connected to the object to be balanced, and the other end connected to an anchoring foundation on the seabed; it also includes:

[0028] A positioning unit installed on the object to be balanced is used to monitor the displacement and motion status of the object in real time.

[0029] The controller is used to predict the displacement of the object to be balanced at the next moment based on the displacement data collected by the positioning unit; and to calculate the total restoring force vector required to restore the object to the equilibrium position based on the predicted displacement; and to decompose the total restoring force vector into control commands for each tensioning actuator.

[0030] The tensioning actuator corresponds one-to-one with the mooring cable and is used to adjust the tension state of the corresponding mooring cable according to control commands.

[0031] Taking the object to be balanced as a floating platform as an example, such as Figure 1As shown, the mooring cable array in this embodiment uses three mooring cables. One end of each cable is evenly distributed outside the ballast tank or buoy of the floating platform via a universal joint, while the other end extends to the seabed and connects to the anchoring foundation. The mooring cables adopt a three-section design: the section closest to the platform is a high-strength synthetic fiber cable to provide good elasticity and reduce self-weight; the middle and bottom sections are anchor chains to provide gravity stiffness.

[0032] The positioning unit is installed on the floating wind turbine platform to measure the platform's six degrees of freedom motion data in real time and at high frequency (e.g., above 10Hz), especially the sway and roll displacement in the horizontal plane. The positioning unit can be a combined navigation system based on DGPS (Differential Global Positioning System), RTKGPS (Real-time Dynamic Carrier Phase Differential Technology) and combined with IMU (Inertial Measurement Unit). In this embodiment, a combined navigation system is used, with the RTKGPS receiver achieving centimeter-level positioning accuracy and a sampling frequency of 20Hz; the IMU sampling frequency is 100Hz.

[0033] The controller communicates with the positioning unit and all tensioning actuators. It includes a displacement prediction algorithm module and a mooring force decision module. The displacement prediction algorithm module predicts the displacement of the object to be balanced at the next moment based on the displacement data collected by the positioning unit. The mooring force decision module calculates the total restoring force vector required to restore the object to its equilibrium position based on the predicted displacement and decomposes the total restoring force vector into control commands for each tensioning actuator. The controller uses an industrial-grade embedded real-time controller, running VxWorks or Linux with PreemptRT real-time operating system to ensure the accuracy of the control cycle. The control cycle is set to 50ms.

[0034] The tensioning actuator, preferably a hydraulic cylinder, electric servo cylinder, or linear motor driven actuator, is connected in series between the platform cable guide hole and the mooring cable. The actuator incorporates high-precision displacement and pressure sensors. Its core function is to receive control signals and quickly and accurately adjust the extension and retraction of its piston rod, thereby changing the effective length and tension of the corresponding mooring cable.

[0035] Displacement prediction allows for early detection and proactive intervention of motion trends, avoiding passive responses after deviations occur. This more effectively suppresses deviations, reduces maximum displacement, and improves system stability and safety. By reducing the platform's motion amplitude, dynamic loads and fatigue damage to the tower root, nacelle components, and the mooring system itself can be significantly reduced, thereby extending the overall service life of the floating wind turbine. Independent control of the tension of each mooring cable breaks the isotropic limitation of traditional mooring systems. It can focus on strengthening the mooring stiffness in specific directions under extreme loads, providing stronger directional restoring force, while maintaining relative relaxation in other directions, achieving on-demand distribution of mooring stiffness. Compared to fully active systems requiring continuous thrust output (such as propellers), this invention only requires small-scale tension / release adjustments to the mooring cables when needed, resulting in extremely low energy consumption and better meeting the economic requirements of long-term, unmanned operation of floating wind turbines.

[0036] Correspondingly, this embodiment also provides a semi-active mooring recovery device control method, applied to a semi-active mooring recovery device, such as... Figure 2 As shown, it includes:

[0037] The displacement data sequence of the object to be balanced is acquired in real time, and the displacement of the object to be balanced at the next moment is predicted based on the acquired displacement data sequence. The total restoring force vector required to restore the object to the equilibrium position is calculated based on the predicted displacement. The total restoring force vector is decomposed into control commands for each tensioning actuator. The tensioning actuator adjusts the tension state of the corresponding mooring cable according to the control commands.

[0038] This invention preferably employs a displacement prediction model based on third-order difference autoregression. Its core lies not only in utilizing the current displacement but also in deeply mining the motion trends (velocity and acceleration) implied by the displacement information from the previous two moments. The specific prediction model is as follows:

[0039] ,in, This is the predicted displacement vector at time k+1. , , These are the actual displacement vectors at times k, k-1, and k-2, respectively. Represents the current velocity vector (first-order difference); The current acceleration vector (second-order difference) is represented by the platform's horizontal acceleration vector at time k, directly measured by the IMU. This vector is used to correct the prediction model in real time, improving prediction accuracy under rapidly changing environments. These are weighting coefficients, corresponding to the contribution of the velocity term, acceleration term, and measured acceleration term, respectively. These coefficients can be calibrated and optimized through prior water tank experiments or numerical simulations.

[0040] When performing displacement prediction, the current displacement, the displacement of the previous two moments, and the real-time acceleration are integrated. This method is more accurate than simple linear extrapolation or single-parameter prediction methods, and can better capture the nonlinear characteristics of wind turbine motion, resulting in higher prediction accuracy.

[0041] Furthermore, it also includes adjusting the weighting coefficients based on the measured displacement values.

[0042] After obtaining the predicted displacement, calculate the required total restoring force vector based on the predicted displacement. The restoring force points towards the equilibrium position, and its magnitude is proportional to the magnitude of the predicted displacement, i.e. Where K is the equivalent mooring stiffness coefficient. Subsequently, the overall restoring force... This is then broken down into the directions of each mooring cable. Considering that mooring cables are typically arranged symmetrically and radially, the principle of force decomposition can be used to calculate the target tension increment that each mooring cable needs to provide. M represents the number of mooring cables, and the goal is to make the resultant force of all the tension increments of the mooring cables on the horizontal plane as close as possible. Finally, the controller will calculate the tension increments of each cable target. This is converted into control commands for the corresponding tensioning actuators (such as the target displacement or target force of the hydraulic cylinder). Upon receiving the command, each tensioning actuator acts within milliseconds to precisely tension or release the corresponding mooring cable, thereby establishing the optimal restoring force field in advance before the wind turbine actually reaches the predicted position.

[0043] The specific control process is as follows:

[0044] 1. Every 50ms, the controller synchronizes and obtains the latest platform position from RTKGPS and IMU. and acceleration .

[0045] 2. The displacement prediction algorithm module calls the displacement data of the first two cycles stored in memory. and .

[0046] 3. Perform calculations based on the prediction model. For example, after preliminary simulation calibration, the weighting coefficients are set to... .but: , ; obtain the predicted displacement .

[0047] 4. The mooring force decision module calculates the required restoring force: , , It can adaptively adjust according to sea conditions, using a larger K value in severe sea conditions.

[0048] 5. Assume the angles between the three mooring cables and the positive x-axis are respectively... The tension increment of each cable target is calculated by solving the following system of linear equations:

[0049] ,

[0050] This is an underdetermined system of equations with multiple solutions. An optimization algorithm can be used to find the optimal solution while satisfying the resultant force requirement and pursuing objectives such as minimizing total energy consumption or achieving optimal tension balance among the cables. .

[0051] 6. The controller will The control signal is sent to each actuator through the hydraulic servo valve. The actuator moves quickly to adjust the position of the piston rod, so that the tension of the corresponding mooring cable changes to the target value.

[0052] Through the cyclical execution of the above process, the semi-active mooring device in this embodiment can effectively maintain a more stable position for the floating wind turbine in wind and waves.

[0053] The system and method provided by this invention are applicable not only to floating wind turbine platforms, but also to other floating offshore structures.

Claims

1. A semi-active recovery mooring arrangement comprising an array of mooring lines, one end of which is connected to a body to be balanced and the other end of which is connected to a seabed anchoring foundation, characterised in that, Also includes: A positioning unit installed on the object to be balanced is used to monitor the displacement and motion status of the object in real time. The controller is used to predict the displacement of the object to be balanced at the next moment based on the displacement data collected by the positioning unit; and to calculate the total restoring force vector required to restore the object to the equilibrium position based on the predicted displacement; and to decompose the total restoring force vector into control commands for each tensioning actuator. The tensioning actuator corresponds one-to-one with the mooring cable and is used to adjust the tension state of the corresponding mooring cable according to control commands.

2. Semi-active recovery mooring according to claim 1, characterized in that The tensioning actuator is a hydraulic servo actuator, an electric servo cylinder, or a linear motor actuator.

3. A semi-active recovery mooring according to claim 1, characterised in that, The object to be balanced is a floating wind turbine platform.

4. The semi-active recovery mooring of claim 1, wherein, The positioning unit employs a combined navigation system that integrates real-time dynamic carrier phase differential technology and an inertial measurement unit.

5. The semi-active mooring recovery device according to claim 1, characterized in that, The mooring cable is connected to the object to be balanced via a universal joint.

6. A semi-active mooring recovery device control method, applied to the semi-active mooring recovery device according to any one of claims 1-5, characterized in that, include: The displacement data sequence of the object to be balanced is collected in real time, and the displacement of the object to be balanced at the next moment is predicted based on the collected displacement data sequence. The total restoring force vector required to restore the object to its equilibrium position is calculated based on the predicted displacement; the total restoring force vector is then decomposed into control commands for each tensioning actuator. The tensioning actuator adjusts the tension of the corresponding mooring cable according to the control command.

7. The semi-active mooring recovery device control method according to claim 6, characterized in that, The specific method for predicting the displacement of the object to be balanced at the next moment based on the collected displacement data sequence is as follows: ,in, This is the predicted displacement vector at time k+1. , , Let be the actual displacement vectors at times k, k-1, and k-2, respectively. Let be the acceleration vector at time k. These are the weighting coefficients.

8. The semi-active mooring recovery device control method according to claim 7, characterized in that, Also includes: The weighting coefficients are adjusted based on the measured displacement values.

9. The semi-active mooring recovery device control method according to claim 6, characterized in that, When decomposing the total restoring force vector into control commands for each tensioning actuator, it also includes obtaining the optimal control command with the goal of minimizing total energy consumption or achieving the most balanced tension in each cable.

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